CP HiCache ownership is page-granular, so a backed radix node must not be split inside a padded physical tail page. When a shorter hit would require an interior tail-page boundary, matching now floors to the previous page boundary and sacrifices the sub-page cache prefix instead of splitting ownership metadata.
Constraint: Host/device/draft CP HiCache metadata tracks page owners and padded physical spans.
Rejected: Split one padded tail page across two radix nodes | it would require half-page ownership semantics and risks double-counting capacity.
Confidence: high
Scope-risk: moderate
Directive: Keep exact valid-tail hits, but floor partial backed-node splits to page boundaries unless metadata gains explicit sub-page ownership.
Tested: Remote py_compile for hiradix_cache.py and test_cp_hicache_metadata.py in g0034 container.
Tested: Remote pytest targeted backed-tail split tests plus exact valid-tail hit test: 3 passed.
Tested: Remote pytest test_cp_hicache_metadata.py test_cp_hicache_load_back_owner_lanes.py: 92 passed, 5 warnings.
Not-tested: Live ETE traffic under divergent short-prefix prompts.
Co-authored-by: OmX <omx@oh-my-codex.dev>
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